Within less than two days, I watched England and France play football (though not, as you may recall, against each other), saw the John Constable exhibition at Tate Britain and went to the Cezanne centenary exhibition in Aix-en-Provence. What a gift schedule for a columnist, I thought. What symmetry, and what an easy way into one of those complicated comparisons loved by commentators and irritating to everyone else. This one's a cinch. After all, is not Rooney the Constable of English soccer, and Cezanne the Zidane of Impressionism? Or indeed, the other way round? On the other hand, perhaps not.

The combined soccer-and-painting contest was an emphatic 2-0 triumph for France, the football for obvious reasons, the art because, apart from the obvious difference between a painter of genius and one of minor excellence, the Constable exhibition was such an unsatisfying event, for one particular reason. It was, admittedly, the first time that his large canvasses - his six-footers - had been shown next to the equally vast sketches he had made in preparation. As a result, the accompanying labelling was obsessed with pointing out how the final product had developed from the sketches. I felt, after a while, that I was not there to appreciate the artist, merely to spot the differences. At the Cezanne show, one just looked and marvelled. No explanations were needed.

France's World Cup win over Brazil has clearly, if only temporarily, lifted the cloud of pessimism and morosity that has dominated the nation for so long. But I have difficulty in accepting the theory being peddled that such a joyous event (to be added to if France win the cup) has any effect on the popularity of its politicians. The French are not stupid enough to think that Chirac and De Villepin are somehow responsible for the exploits of Zidane and Henry, and that the beleaguered prime minister will suddenly be seen in a better light as the goals keep coming.

Tony Blair, it was said, was fervently hoping for an English victory to reverse his, and the government's, growing unpopularity. How would it have done that, assuming England had done better? "Yes, he did a terrible thing taking us into the war with Iraq, but now that we've won a few football matches it doesn't seem so bad. I wasn't going to vote Labour next time round, but Gerrard's winning goal changes my mind." Unlikely.

Will the lack of success finally dash Blair's chances of being well thought of, or even give an electoral advantage to David Cameron? A ludicrous thought. Besides, I've seen no signs of a deep slump in national morale. Fed up, yes; cross with Eriksson or Rooney, yes. That's about it.

People keep battering me with the example that Harold Wilson lost the 1970 general election to Edward Heath just four days after England lost their World Cup quarter-final match against West Germany, 3-2. Factually true, but it's stretching it to believe that Wilson would have won if England had. And there are still many who believe that England's 1966 World Cup won Wilson that year's election. The slight difficulty with that argument is that the election was four months before the football.

Angela Merkel and Romano Prodi are alleged to be using their countries' successful World Cup campaigns to do more than just boost their own popularity. Each is accused of smuggling through unpopular laws while the attention of parliamentarians and the people is elsewhere. Not much of a tribute to democracy, that.

What a great fuss was made over the fact that the difficult Romanian diva Angela Gheorghiu was coming to the Royal Opera House to sing Tosca in a brand new production. And what a disappointment she turned out to be. I wasn't too surprised. I have seen her perform live in the past, not to my satisfaction. I didn't expect her Tosca to be wonderful, took no steps to see it, and was comforted by the near unanimity, among newspaper critics and opera-goers alike, that she wasn't quite up to it. The pre-opening hype that Gheorghiu was somehow about to inherit Maria Callas's mantle of Tosca greatness was shown to be absurd within a few notes of her opening her lungs.

But I'm fond of the Puccini opera, and last week went to the same, superb production - with not a Gheorghiu in sight. Instead, there was a "second cast", insultingly known in the trade as the B-cast, with Tosca sung by an American, Catherine Nagelstad, of whom I had not previously heard. She was terrific in every way.

I overheard a chap who had seen Gheorghiu the week before tell his companion that Nagelstad had been far better. But I did not read any reviews of her outstanding performance in the papers. There weren't any. The Romanian had captured not only all the anticipatory publicity, but all the review space as well. She sang in only five of the 12 performances, but received near enough 100% of the attention. Even had she delivered satisfaction - which she didn't - it would have been unfair.

My question is: how does the public get to know that Nagelstad is good? Obviously, the insiders are aware of her, or she would not have been asked to sing Tosca at all; and her CV shows that she has performed in many opera houses all over the world. That's not the point. The British opera-loving public, other than those who happened to be present at Covent Garden, most of them disappointed (at least initially) because they weren't quick enough to get tickets for Gheorghiu, is ignorant of her.

The basic difficulty is that newspaper critics these days rarely cover second casts. I'm not criticising them. It's not their fault. It used to be different, I'm told. Philip Hope-Wallace, for instance, one of the foremost opera critics of the 60s, always did so - and the Guardian always gave him the space. And it is space that is at the heart of the problem today. Few arts editors of newspapers would countenance two reviews of the same opera within a couple of weeks. As it is, many worthy opera and concert performances (which tend to fight for the same space) don't get reviewed at all. The move to tabloid-size papers has exacerbated the shortage of space for critics.

At the same time, critics are faced with a choice of more productions than ever before. How can they justify writing about the same one twice? Some try, but rarely succeed. I don't have an answer, but I do know that Catherine Nagelstad deserves better. So does the public.

· This week Marcel re-read, as he does every summer, The Leopard, by Giuseppe di Lampedusa: "One of the most evocative, poignant, elegaic and melancholic portrayals of lost love and lost values, and much shorter than Anna Karenina." He listened to a compilation of George Gershwin playing his compositions: "He's not always the best interpreter of his own music."